Pharmaceutical excipient having improved compressibility

ABSTRACT

A composition, comprising (a) microcrystalline cellulose; and (b) a compressibility augmenting agent which (i) physically restricts the proximity of the interface between adjacent cellulose surfaces; or (ii) inhibits interactions between adjacent cellulose surfaces; or (iii) accomplishes both (i) and (ii) above, is disclosed. The composition is in the form of agglomerated particles of microcrystalline cellulose and the compressibility augmenting agent in intimate association with each other.

BACKGROUND OF THE INVENTION

This is a continuation-in-part of U.S. application Ser. No. 08/660,553filed Jun. 10, 1996, now U.S. Pat. No. 5,866,166 U.S. application Ser.No. 08/486,183, filed Jun. 7, 1995 now U.S. Pat. No. 5,725,883 and U.S.application Ser. No. 08/724,613 filed Sep. 30, 1996, now U.S. Pat. No.5,725,884, which is a continuation of U.S. application Ser. No.08/370,576, filed Jan. 9, 1995, now U.S. Pat. No. 5,585,115. The entiredisclosures of U.S. application Ser. Nos. 08/660,553, 08/486,183,08/724,613, and 08/370,576 are hereby incorporated by reference.

The present invention relates to a novel excipient for use in themanufacture of pharmaceuticals, and in particular, solid dosage formssuch as tablets which include one or more active ingredients.

In order to prepare a solid dosage form containing one or more activeingredients (such as drugs), it is necessary that the material to becompressed into the dosage form possess certain physical characteristicswhich lend themselves to processing in such a manner. Among otherthings, the material to be compressed must be free-flowing, must belubricated, and, importantly, must possess sufficient cohesiveness toinsure that the solid dosage form remains intact after compression.

In the case of tablets, the tablet is formed by pressure being appliedto the material to be tableted on a tablet press. A tablet pressincludes a lower punch which fits into a die from the bottom and a upperpunch having a corresponding shape and dimension which enters the diecavity from the top after the tableting material fills the die cavity.The tablet is formed by pressure applied on the lower and upper punches.The ability of the material to flow freely into the die is important inorder to insure that there is a uniform filling of the die and acontinuous movement of the material from the source of the material,e.g. a feeder hopper. The lubricity of the material is crucial in thepreparation of the solid dosage forms since the compressed material mustbe readily ejected from the punch faces.

Since most drugs have none or only some of these properties, methods oftablet formulation have been developed in order to impart thesedesirable characteristics to the material(s) which is to be compressedinto a solid dosage form. Typically, the material to be compressed intoa solid dosage form includes one or more excipients which impart thefree-flowing, lubrication, and cohesive properties to the drug(s) whichis being formulated into a dosage form.

Lubricants are typically added to avoid the material(s) being tabletedfrom sticking to the punches. Commonly used lubricants include magnesiumstearate and calcium stearate. Such lubricants are commonly included inthe final tableted product in amounts of less than 1% by weight.

In addition to lubricants, solid dosage forms often contain diluents.Diluents are frequently added in order to increase the bulk weight ofthe material to be tableted in order to make the tablet a practical sizefor compression. This is often necessary where the dose of the drug isrelatively small.

Another commonly used class of excipients in solid dosage forms arebinders. Binders are agents which impart cohesive qualities to thepowdered material(s). Commonly used binders include starch, and sugarssuch as sucrose, glucose, dextrose, and lactose.

Disintegrants are often included in order to ensure that the ultimatelyprepared compressed solid dosage form has an acceptable disintegrationrate in an environment of use (such as the gastrointestinal tract).Typical disintegrants include starch derivatives and salts ofcarboxymethyl cellulose.

There are three general methods of preparation of the materials to beincluded in the solid dosage form prior to compression: (1) drygranulation; (2) direct compression; and (3) wet granulation.

Dry granulation procedures may be utilized where one of theconstituents, either the drug or the diluent, has sufficient cohesiveproperties to be tableted. The method includes mixing the ingredients,slugging the ingredients, dry screening, lubricating and finallycompressing the ingredients.

In direct compression, the powdered material(s) to be included in thesolid dosage form is compressed directly without modifying the physicalnature of the material itself.

The wet granulation procedure includes mixing the powders to beincorporated into the dosage form in, e.g., a twin shell blender ordouble-cone blender and thereafter adding solutions of a binding agentto the mixed powders to obtain a granulation. Thereafter, the damp massis screened, e.g., in a 6- or 8-mesh screen and then dried, e.g., viatray drying, the use of a fluid-bed dryer, spray-dryer, radio-frequencydryer, microwave, vacuum, or infra-red dryer.

The use of direct compression is limited to those situations where thedrug or active ingredient has a requisite crystalline structure andphysical characteristics required for formation of a pharmaceuticallyacceptable tablet. On the other hand, it is well known in the art toinclude one or more excipients which make the direct compression methodapplicable to drugs or active ingredients which do not possess therequisite physical properties. For solid dosage forms wherein the drugitself is to be administered in a relatively high dose (e.g., the drugitself comprises a substantial portion of the total tablet weight), itis necessary that the drug(s) itself have sufficient physicalcharacteristics (e.g., cohesiveness) for the ingredients to be directlycompressed.

Typically, however, excipients are added to the formulation which impartgood flow and compression characteristics to the material as a wholewhich is to be compressed. Such properties are typically imparted tothese excipients via a pre-processing step such as wet granulation,slugging, spray drying, spheronization, or crystallization. Usefuldirect compression excipients include processed forms of cellulose,sugars, and dicalcium phosphate dihydrate, among others.

A processed cellulose, microcrystalline cellulose, has been utilizedextensively in the pharmaceutical industry as a direct compressionvehicle for solid dosage forms. Microcrystalline cellulose iscommercially available under the tradename EMCOCEL® from Edward MendellCo., Inc. and as Avicel® from FMC Corp. Compared to other directlycompressible excipients, microcrystalline cellulose is generallyconsidered to exhibit superior compressibility and disintegrationproperties.

Another limitation of direct compression as a method of tabletmanufacture is the size of the tablet. If the amount of activeingredient is high, a pharmaceutical formulator may choose to wetgranulate the active with other excipients to attain an acceptably sizedtablet with the desired compact strength. Usually the amount offiller/binder or excipients needed in wet granulation is less than thatrequired for direct compression since the process of wet granulationcontributes to some extent toward the desired physical properties of atablet. Thus, despite the advantages of direct compression (such asreduced processing times and costs), wet granulation is widely used inthe industry in the preparation of solid dosage forms. Many of thoseskilled in the art prefer wet granulation as compared to directcompression because this method has a greater probability of overcomingany problems associated with the physical characteristics of the variousingredients in the formulation, thereby providing a material which hasthe requisite flow and cohesive characteristics necessary to obtain anacceptable solid dosage form.

The popularity of the wet granulation process as compared to the directcompression process is based on at least three advantages. First, wetgranulation provides the material to be compressed with better wettingproperties, particularly in the case of hydrophobic drug substances. Theaddition of a hydrophilic excipient makes the surface of a hydrophobicdrug more hydrophilic, easing disintegration and dissolution. Second,the content uniformity of the solid dosage forms is generally improved.Via the wet granulation method, all of the granules thereby obtainedshould contain approximately the same amount of drug. Thus, segregationof the different ingredients of the material to be compressed (due todifferent physical characteristics such as density) is avoided.Segregation is a potential problem with the direct compression method.Finally, the particle size and shape of the particles comprising thegranulate to be compressed are optimized via the wet granulationprocess. This is due to the fact that when a dry solid is wetgranulated, the binder "glues" particles together, so that theyagglomerate in the granules which are more or less spherical.

Due to the popularity of microcrystalline cellulose, pharmaceuticalformulators have deemed it desirable to include this excipient in aformulation which is wet granulated prior to tableting. Unfortunately,currently-available microcrystalline cellulose does not hold to thetypical principle that the amount of filler/binder needed in wetgranulation is less than that in direct compression. It is known thatthe exposure of the microcrystalline cellulose to moisture in the wetgranulation process severely reduces the compressibility of thisexcipient. The loss of compressibility of microcrystalline cellulose isparticularly problematic where the formulation dictates that the finalproduct will be relatively large in the environment of use. For example,if a pharmaceutical formulator desires to prepare a solid oral dosageform of a high dose drug, and the use of the wet granulation techniqueis deemed necessary, the loss of compressibility of the microcrystallinecellulose dictates that a larger amount of this material may be neededto obtain an acceptably compressed final product. The additional amountof microcrystalline cellulose needed adds cost to the preparation, butmore importantly adds bulk, making the product more difficult toswallow.

The loss of compressibility of microcrystalline cellulose when exposedto wet granulation has long been considered a problem in the art forwhich there has been no satisfactory solution.

Attempts have been made to provide an excipient having highcompressibility, a small bulk (high apparent density), and goodflowability, while being capable of providing satisfactorydisintegration of the solid dosage form, which is applicable to wetgranulation as well as to dry granulation and direct compression methodsfor preparation of solid dosage forms.

For example, U.S. Pat. No. 4,159,345 (Takeo, et al.) describes anexcipient which consists essentially of a microcrystalline cellulosehaving an average degree of polymerization of 60 to 375 and obtainedthrough acid hydrolysis or alkaline oxidative degradation of acellulosic substance selected from linters, pulps and regeneratedfibers. The microcrystalline cellulose is said to be a white cellulosicpowder having an apparent specific volume of 1.6-3.1 cc/g, a reposeangle of 35° to 42°, a 200-mesh sieve residue of 2 to 80% by weight anda tapping apparent specific volume of at least 1.4 cc/g.

In U.S. Pat. No. 4,744,987 (Mehra, et al.), a particulate co-processedmicrocrystalline cellulose and calcium carbonate composition isdescribed wherein the respective components are present in a weightratio of 75:25 to 35:65. The co-processed composition is said to beprepared by forming a well-dispersed aqueous slurry of microcrystallinecellulose and calcium carbonate and then drying the slurry to yield aparticulate product. The combination of these two ingredients is said toprovide a lower cost excipient which has tableting characteristicssimilar to those of microcrystalline cellulose and which would satisfy aneed for an economical excipient with good performance that is desiredby the vitamin market.

European Patent Application EP 0609976A1 (assigned to Asahi KaseiKabushiki Kaisha) describes an excipient comprising white powderymicrocrystalline cellulose having an average degree of polymerization offrom 100 to 375, preferably from 190 to 210, and an acetic acid holdingcapacity of 280% or more, preferably from 290 to 370%. The excipient issaid to exhibit high compactability and a high rate of disintegrationand is said to be obtained by heat-treating an aqueous dispersion ofpurified cellulose particles, which has a solids content of 40% or lessby weight, at 100° C. or more, followed by drying, or by subjecting anaqueous dispersion of purified cellulose particles having a solidscontent of 23% or less by weight to thin film-forming treatment anddrying the resultant thin film. The excipient is said to possess a highcompressibility, and a good balance of compactability and rate ofdisintegration.

There still remains a need in the industry for a pharmaceuticalexcipient which possesses excellent compressibility whether utilized ina direct compression or wet granulation procedure.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an excipient whichis useful in a variety of applications, and which may be utilized indirect compression or wet granulation methods.

It is a further object of the present invention to provide an excipientuseful in direct compression methods which has improved compressibilityrelative to microcrystalline cellulose.

It is a further object of the present invention to provide an excipientuseful in wet granulation methods which has improved compressibilityrelative to microcrystalline cellulose.

It is a further object of the present invention to provide afree-flowing excipient which has excellent compressibility propertieswhen utilized in direct compression or wet granulation methods, andwhich furthermore possesses pharmaceutically acceptable disintegrationproperties.

It is a further object of the present invention to provide afree-flowing excipient which has excellent compressibility propertieswhen utilized in direct compression or wet granulation methods, andwhich furthermore possesses pharmaceutically acceptable absorptiveproperties, e.g. enhanced bioavailability of the active agent from thegastrointestinal tract.

It is a further object of the present invention to provide an improvedmicrocrystalline cellulose excipient in which the microcrystallinecellulose has not been chemically altered, and which has improvedcompressibility relative to "off-the-shelf" commercially availablemicrocrystalline cellulose.

It is a further object of the present invention to provide a soliddosage form which includes one or more active agents and the improvedmicrocrystalline cellulose excipient of the present invention.

It is a further object of the present invention to provide an oral soliddosage form for one or more drugs which is economical to manufacture,which maintains its integrity during storage, and which possessesexcellent disintegration and dissolution properties when exposed, e.g.,to gastrointestinal fluid.

In accordance with the above objects and others which will be obvious tothose skilled in the art, the present invention is directed to anexcipient comprising a particulate agglomerate of coprocessedmicrocrystalline cellulose and a compressibility augmenting agent. Thenovel agglomerated excipient preferably possesses compressibility atleast equal to that of commercial grade microcrystalline cellulose, andpreferably superior to that of commercial grade microcrystallinecellulose, when dry mixed or wet granulated with an active agent, otheroptional pharmaceutical additives and compressed into solid dosageforms.

The relative amount of compressibility augmenting agent coprocessed withthe microcrystalline cellulose is dependent, in part, upon the type ofcompressibility augmenting agent selected. For purposes of the presentinvention, the amount is generally described as an effective amount,i.e. an amount which enhances or augments the compressibility of themicrocrystalline cellulose. However, one skilled in the art willappreciate that in certain embodiments of the invention where improvedor equal compressibility is not crucial to the preparation of the finalsolid dosage form, the agglomerated excipient may include an amount ofaugmenting agent which may not favorably affect compressibility but mayinstead impart a different beneficial result to the final product.

The microcrystalline cellulose and compressibility augmenting agent arein intimate association with each other, and the compressibilityaugmenting agent portion of the agglomerate is in the form of an aqueoussolution or slurry prior to being coprocessed with microcrystallinecellulose.

The present invention is further directed to an agglomerated excipientwhich is derived from the aqueous slurry. The agglomerated excipient,which includes microcrystalline cellulose, at least one compressibilityaugmenting agent, and other optional ingredients, is dried in a mannerwhich inhibits the formation of hydrogen bonds in the microcrystallinecellulose(intra-molecular and/or inter-molecular bonding). In otherwords, the compressibility augmenting agent is capable, during thedrying of the aqueous slurry, of restricting the close approach ofcellulose surfaces to each other by physically preventing these surfacesfrom approaching each other; or by changing the environment betweenthese surfaces from an environment which tends to promotesurface-to-surface interactions (such as hydrogen-bonding) to anenvironment which tends to inhibit such surface-to-surface interactionsbetween surfaces of the microcrystalline cellulose. In certainembodiments, the compressibility of the microcrystalline cellulose isimproved by utilizing one or more agents which are capable of both ofthese interactions with the microcrystalline cellulose.

Compressibility augmenting agents which create physical barriers betweenmicrocrystalline cellulose surfaces include silicon dioxide having avery fine particle size, e.g., from about 1 nm to about 100 μm. A mostpreferred silicon dioxide is colloidal silicon dioxide. Other materialsof similar size may also be used instead of silicon dioxide to createthe aforementioned physical barrier. In certain preferred embodiments,such other physically-acting compressibility augmenting agents will haveat least some physical characteristics similar to that of silicondioxide.

Compressibility augmenting agents which inhibit surface-to-surfaceinteractions between surfaces of the microcrystalline cellulose includeany material which has the ability, via a portion of the molecule, tobind or interact with the surface of the microcrystalline cellulose andat the same time, via another portion of the molecule, to inhibit theattraction of the cellulose surfaces, e.g., via a hydrophobic portion or"tail". Suitable compressibility augmenting agents will have an HLBvalue of at least 10, preferably at least about 15, and more preferablyfrom about 15 to about 40 or greater. To date, compressibilityaugmenting agents which have shown the greatest effect have hadrelatively high HLB values, and therefore an HLB value from about 30 toabout 40 or greater is most preferred. Agents which exhibit theseproperties include certain surfactants such as sodium lauryl sulfate andpolysorbate 40, and highly polar compounds, including pharmaceuticallyacceptable dyes such as congo red.

The present invention is further directed to an aqueous slurry useful inthe preparation of a compressible excipient useful in dry and wetgranulation formulation methods, comprising a mixture ofmicrocrystalline cellulose and compressibility augmenting agent. Thesolids content of the aqueous slurry is from about 0.5% to about 25%, byweight, preferably from about 15% to about 20% by weight, and mostpreferably from about 17% to about 19% by weight.

The present invention is further directed to a mixture of an activeingredient(s) and an excipient comprising a particulate agglomerate ofcoprocessed microcrystalline cellulose and a compressibility augmentingagent. The microcrystalline cellulose and compressibility augmentingagent are in intimate association with each other and the ratio ofactive ingredient to excipient is from about 1:99 to about 99:1, byweight.

The present invention is further directed to a granulate of an activeagent and the novel excipient described herein, wherein the active agentand excipient have been subjected to a wet granulation procedure.

The present invention is also directed to a compressed solid dosage formcomprising an active ingredient(s) and the novel excipient describedherein, wherein the active agent and excipient have been directlycompressed into the solid dosage form or have been subjected to a wetgranulation procedure and thereafter compressed into the solid dosageform. The compressed solid dosage form provides a suitable releasedissolution profile of the active ingredient(s) when exposed to aqueoussolutions during in-vitro dissolution testing, and provides a release ofdrug in an environment of use which is considered bioavailable. In oneembodiment of the invention, the dissolution profile of the solid dosageform is suitable for immediate release of the active agent. In furtherembodiments of the invention, the dissolution profile of the soliddosage form is modified to provide a controlled or sustained releasedissolution profile.

The present invention is further directed to a method of maintainingand/or enhancing the compressibility of microcrystalline cellulose. Themethod includes forming an aqueous slurry containing a mixture ofmicrocrystalline cellulose and a compressibility augmenting agent, anddrying the slurry to obtain microcrystalline cellulose-based excipientparticles in which the compressibility augmenting agent has beenintegrated with the microcrystalline cellulose particles. Within thisaspect of the invention, the slurry contains from about 0.5% to about25% by weight microcrystalline cellulose, with amounts of from about 15%to about 20% being preferred. The novel excipient described herein isfree-flowing, possesses excellent disintegration and/or absorptiveproperties, and importantly, in certain embodiments possesses improvedcompressibility relative to normal "off-the-shelf" commerciallyavailable microcrystalline cellulose when directly compressed. Theadvantages of the novel excipient described herein are especiallyrealized in pharmaceutical formulations prepared using wet granulationtechniques. When utilized in wet granulation techniques, the novelexcipient surprisingly provides a compressibility which is substantiallyimproved in preferred embodiments in comparison to the compressibilityof normal "off-the-shelf" commercially available microcrystallinecellulose used in wet granulation and is even comparable to"off-the-shelf" microcrystalline cellulose used in direct compressiontechniques. In other embodiments, the novel excipient surprisinglyprovides a compressibility which is substantially superior to thecompressibility of normal "off-the-shelf" commercially availablemicrocrystalline cellulose used in direct compression techniques.

Accordingly, the novel agglomerated of the invention provides enhancedmaterial flow properties and direct compression compactibility comparedto regular microcrystalline cellulose. The enhanced compactibility hasbeen shown to allow for the production of satisfactory tablets, evenwith poorly compactible drugs, reduction in tablet size for various highdose drug formulations, and, in general, enhancement of the drug contentuniformity of tableted dosage forms, especially in high speed tableting.

The term "environmental fluid" is meant for purposes of the invention toencompass, e.g., an aqueous solution, or gastrointestinal fluid.

By "bioavailable" it is meant for purposes of the invention that thetherapeutically active medicament is absorbed from the solid dosage formwhich includes the novel agglomerated excipient of the invention, andbecomes available in the body at the intended site of drug action.

By "surfactant" it is meant for purposes of the present invention thatthe material is a surface active agent which displays wetting, detergentor soap-like qualities as those agents are understood by those ofordinary skill in the art.

The benefits of the novel agglomerated microcrystalline celluloseexcipients of the invention include higher direct compressioncompactibility (which in turn provides harder, less friable tablets,reduces binder usage/cost, reduces tablet size, and accommodates poorlycompactible active ingredients), and enhanced material flow (which inturn provides better content uniformity, allows higher speed tableting,and accommodates poorly flowing drugs); and preservation ofcompactibility in a wet granulation (which in turn reduces formulationdevelopment time and cost, reduces binder usage/cost, avoidsextra-granular processing/cost, and reduces tablet size).

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of embodiments of the inventionand are not meant to limit the scope of the invention as encompassed bythe claims.

FIG. 1 graphically shows a comparison of the tensile strength of tabletsprepared in accordance with the invention and (compressibilityaugmenting agent=silicon dioxide) prior art tablets.

FIG. 2 graphically shows a comparison of the tensile strength of APAPcontaining tablets prepared in accordance with the invention and priorart APAP containing tablets.

FIG. 3 graphically shows a comparison of the tensile strength of tabletsprepared in accordance with the invention to contain microcrystallinecellulose coprocessed with diatomaceous earth, tablets containingmicrocrystalline cellulose coprocessed with 2% w/w SiO₂ and prior arttablets prepared to contain only unmodified microcrystalline cellulose.

FIG. 4 graphically illustrates a comparison of the tensile strength oftablets prepared W using microcrystalline cellulose coprocessed withsilica gel, tablets prepared with the novel coprocessed microcrystallinecellulose and tablets prepared with microcrystalline cellulose alone.

FIG. 5 graphically illustrates a comparison of the tensile strength oftablets prepared using microcrystalline cellulose coprocessed with HS 5grade SiO₂, tablets prepared using coprocessed microcrystallinecellulose-SiO₂ and prior art tablets prepared to contain only unmodifiedmicrocrystalline cellulose.

FIG. 6 graphically shows a comparison of the tensile strength of tabletsprepared in accordance with the invention (compressibility augmentingagent=surfactant) and prior art tablets.

FIG. 7 graphically shows a comparison of the tensile strength of tabletsprepared in accordance with the invention to contain microcrystallinecellulose coprocessed with sodium lauryl sulfate, tablets containingmicrocrystalline cellulose coprocessed with docusate sodium and priorart tablets prepared to contain only unmodified microcrystallinecellulose.

FIG. 8 graphically illustrates a comparison of the tensile strength oftablets prepared using microcrystalline cellulose coprocessed withpolysorbate 40, tablets prepared with the novel sodium lauryl sulfatecoprocessed microcrystalline cellulose and tablets prepared withmicrocrystalline cellulose alone.

FIG. 9 graphically illustrates a comparison of the tensile strength oftablets prepared using microcrystalline cellulose coprocessed withpolydimethyl siloxane (simethicone), tablets prepared using coprocessedmicrocrystalline cellulose-sodium lauryl sulfate and prior art tabletsprepared to contain only unmodified microcrystalline cellulose.

DETAILED DESCRIPTION OF THE INVENTION

Excipients of the present invention comprise Microcrystalline Cellulose(MCC) and augmenting agents. Microcrystalline cellulose is a well-knowntablet diluent, binder and disintegrant. Its chief advantage over otherexcipients is that it can be directly compressed into self-bindingtablets which disintegrate rapidly when placed into water. Thiswidely-used ingredient is prepared by partially depolymerizing celluloseobtained as a pulp from fibrous plant material with dilute mineral acidsolutions. Following hydrolysis, the hydrocellulose thereby obtained ispurified via filtration and an aqueous slurry is spray dried to formdry, white odorless, tasteless crystalline powder of porous particles ofvarious sizes. Another method of preparing microcrystalline cellulose isdisclosed in U.S. Pat. No. 3,141,875. This reference disclosessubjecting cellulose to the hydrolytic action of hydrochloric acid atboiling temperatures so that amorphous cellulosic material can beremoved and aggregates of crystalline cellulose are formed. Theaggregates are collected by filtration, washed with water and aqueousammonia and disintegrated into small fragments, often called cellulosecrystallites by vigorous mechanical means such as a blender.Microcrystalline cellulose is commercially available in several gradeswhich range in average particle size from 20 to 200 microns.

Microcrystalline cellulose is water-insoluble, but the material has theability to draw fluid into a tablet by capillary action. The tabletsthen swell on contact and the microcrystalline cellulose thus acts as adisintegrating agent. The material has sufficient self-lubricatingqualities so as to allow a lower level of lubricant as compared to otherexcipients.

Typically, microcrystalline cellulose has an apparent density of about0.28 g/cm³ and a tap density of about 0.43 g/cm³. Handbook ofPharmaceutical Excipients, pages 53-55.

When utilized in pharmaceutical applications, microcrystalline celluloseis typically used as a tablet binder/diluent in wet granulation anddirect compression formulations in amounts of 3-30% of the formulation,or more. However, it is known to use more or less microcrystallinecellulose in pharmaceutical products, depending upon the requirements ofthe formulation.

The novel excipients of the present invention also include one or morecompressibility augmenting agents. The compressibility augmentingagent(s) is present in amounts ranging from about 0.1% to about 50% byweight of microcrystalline cellulose.

Direct compression tablet manufacturing is preferred for many productsin the pharmaceutical industry. It is a simple process involving lessextensive equipment, operating time and cost. Microcrystalline celluloseis a good excipient for direct compression processing.

Microcrystalline cellulose has inherently high compactibility due to itsplastic deformation and limited elastic recovery. Microcrystallinecellulose usually provides for good drug dispersion, even ordered mixingwith some drugs and particular grades of microcrystalline cellulose.However, the material flow properties are relatively poor for mostgrades of microcrystalline cellulose. Intermittent and non-uniform flowcan occur as the formulation moves from the hopper to the die on atablet press. This non-uniform flow can lead to drug content variationsin the finished tableted dosage form.

The popularity of the wet granulation process as compared to the directcompression process is based on at least three potential advantages.First, wet granulation may provide the material to be compacted with amore hydrophilic nature, in order to improve the wetting, disintegrationand dissolution characteristics of some hydrophobic drugs oringredients. Second, the content uniformity and drugsegregation-resistance can be enhanced using a granulation step to lockdrug and excipient components together during blending. Finally, themicrometric characteristics of the component powders can be optimizedprior to compaction, which is often aided by incorporation of apolymeric binder. It is normally considered that this last propertyimbued by wet granulation will yield a significantly more compactibleproduct and consequently stronger, more robust tablets. However, it hasbeen found that the most compactable tableting excipient,microcrystalline cellulose, can lose between 30 and 50% of its tabletstrength enhancing characteristics, following wet granulation.Microcrystalline cellulose tablet weakening caused by wet granulation isobserved in all cases where water is added, although the magnitude ofloss of compactibility is directed related to the concentration of waterused, as well as granulation and drying energetics. This loss ofcompactibility can result in a very significant loss of functionality,generally leading to a requirement for a larger binder concentration inthe formulation and consequently less efficient and more costly tabletproduction as well as larger tablets.

We have found that the reduction in compactibility of microcrystallinecellulose which has been wet granulated is generally accompanied by adecrease in particle porosity, specific surface area available to adsorbnitrogen and also an increase in granule bulk density and friability.However, granule particle size distribution was found to have arelatively minor effect on granule compactibility. Wet granulation hasbeen found to have only a minor effect on the solubility parameters ofmicrocrystalline cellulose. Further, wet granulation does not alter theX-ray diffraction pattern and the Raman and 13C-NMR spectra ofmicrocrystalline cellulose. However, as a result of granulation, theinfrared spectra of microcrystalline cellulose obtained using thetechniques of attenuated total reflectance (ATRIR) and optical IRspectroscopy were altered slightly. This is hypothesized to indicatethat only the near-surface molecular layers may be significantlyinvolved in interactions with water. Granule properties, includingcompactibility, have also been found to be influenced by the amount ofgranulating fluid employed, the duration and rate of wet mass agitation,wet mass storage time before drying, and granule drying technique.Further, granule dewatering by solvent exchange was found to have abeneficial effect on granule compactibility.

It is hypothesized that the granulation-reduced microcrystallinecellulose compactibility is caused at least in significant part byincreasing intraparticle and/or interparticle hydrogen bonding. Forpurposes of the present invention, this phenomenon is termed"quasi-hornification" since, unlike hornification of cellulose fibersdescribed in the literature elsewhere, quasi-hornification ofmicrocrystalline cellulose has not ben observed by us to reduce theability of microcrystalline cellulose to absorb water vapor.Furthermore, quasi-hornified microcrystalline cellulose was found to befully reversible, unlike the hornification which occurs when celluloseis wetted. Microcalorimetry indicates that during adsorption of watervapor by granulated microcrystalline cellulose, the extent ofintraparticle bond disruption is greater than occurring during watervapor adsorption by ungranulated microcrystalline cellulose. Thisprovides evidence to support the theory that granulation results inincreased intraparticle hydrogen bonding, some of which is reversible onadsorption of water vapor.

The present invention is directed in part to a novel agglomeratedmicrocrystalline cellulose excipient which comprises a combination ofmicrocrystalline cellulose as described above together in intimateassociation with a compressibility augmenting agent. The novelagglomerated microcrystalline cellulose excipient is prepared in amanner which significantly reduces the hydrogen bonding between inter-and/or intra-molecular cellulose-to-cellulose bonding which occurs whenregular, commercial grade microcrystalline cellulose is exposed tomoisture (water). This can be accomplished, e.g., by preparing anaqueous slurry of microcrystalline cellulose, compressibility augmentingagent(s), and other optional ingredients, and drying the mixture in amanner which inhibits quasi-hornification.

The novel agglomerated microcrystalline cellulose excipient utilizes acompressibility augmenting agent which

(i) physically restricts the proximity of the interface between adjacentcellulose surfaces;

(ii) inhibits interactions between adjacent cellulose surfaces, forexample, via the creation of a hydrophobic boundary at cellulosesurfaces; or

(iii) accomplishes both (i) and (ii) above.

In one preferred embodiment of the invention, the compressibilityaugmenting agent which provides a physical barrier between adjacentcellulose surfaces is a silicon dioxide. Silicon dioxide is obtained byinsolubilizing dissolved silica in sodium silicate solution. Whenobtained by the addition of sodium silicate to a mineral acid, theproduct is termed silica gel. When obtained by the destabilization of asolution of sodium silicate in such a manner as to yield very fineparticles, the product is termed precipitated silica. Silicon dioxide isinsoluble in water. Prior to the present invention, silicon dioxide, andin particular colloidal silicon dioxide, was used mainly as a glidantand anti-adherent in tableting processes and encapsulation, promotingthe flowability of the granulation. The amount of silicon dioxideincluded in such tablets for those applications is very limited,0.1-0.5% by weight. Handbook of Pharmaceutical Excipients, ©1986American Pharmaceutical Association, page 255. This is due in part tothe fact that increasing the amount of silicon dioxide in the mixture tobe tableted causes the mixture to flow too well, causing a phenomenaknown to those skilled in the tableting art as "flooding". If themixture flows too well, a varying tablet weight with uneven contentuniformity can result.

Those skilled in the art will appreciate that the name and/or method ofpreparation of the silicon dioxide utilized in the present invention isnot determinative of the usefulness of the product. Rather, aspreviously mentioned, it has been surprisingly discovered that it is thephysical characteristics of the silicon dioxide that are critical. Inparticular, it has been discovered that silicon dioxide having arelatively large particle size (and correspondingly small surface area),such as silica gel, is not useful in the preparation of the improvedmicrocrystalline cellulose products of the invention. The appendedclaims are deemed to encompass all forms of silicon dioxide having anaverage primary particle size from about 1 nm to about 100 μm, and/or asurface area from about 10 m² /g to about 500 m² /g.

The silicon dioxide utilized in the invention is of the very fineparticle size variety. In the more preferred embodiments of theinvention, the silicon dioxide utilized is a colloidal silicon dioxide.Colloidal silicon dioxide is a submicron fumed silica prepared by thevapor-phase hydrolysis (e.g., at 1110° C.) of a silicon compound, suchas silicon tetrachloride. The product itself is a submicron, fluffy,light, loose, bluish-white, odorless and tasteless amorphous powderwhich is commercially available from a number of sources, includingCabot Corporation (under the tradename Cab-O-Sil); Degussa, Inc. (underthe tradename Aerosil); E. I. DuPont & Co.; and W. R. Grace & Co.Colloidal silicon dioxide is also known as colloidal silica, fumedsilica, light anhydrous silicic acid, silicic anhydride, and silicondioxide fumed, among others. A variety of commercial grades of colloidalsilicon dioxide are produced by varying the manufacturing process. Thesemodifications do not affect the silica content, specific gravity,refractive index, color or amorphous form. However, these modificationsare known to change the particle size, surface areas, and bulk densitiesof the colloidal silicon dioxide products.

The surface area of the preferred class of silicon dioxides utilized inthe invention ranges from about 50 m² /gm to about 500 m² /gm. Theaverage primary particle diameter of the preferred class of silicondioxides utilized in the invention ranges from about 5 nm to about 50nm. However, in commercial colloidal silicon dioxide products, theseparticles are agglomerated or aggregated to varying extents. The bulkdensity of the preferred class of silicon dioxides utilized in theinvention ranges from about 20 g/l to about 100 g/l.

Commercially available colloidal silicon dioxide products have, forexample, a BET surface area ranging from about 50±15 m² /gm (AerosilOX50) to about 400±20 (Cab-O-Sil S-17) or 390±40 m² l/gm (Cab-O-SilEH-5). Commercially available particle sizes range from a nominalparticle diameter of 7 nm (e.g., Cab-O-Sil S-17 or Cab-O-Sil EH-5) to anaverage primary particle size of 40 nm (Aerosil OX50). The density ofthese products range from 72.0±8 g/l (Cab-O-Sil S-17) to 36.8 g/l (e.g.,Cab-O-Sil M-5). The pH of the these products at 4% aqueous dispersionranges from pH 3.5-4.5. These commercially available products aredescribed for exemplification purposes of acceptable properties of thepreferred class of silicon dioxides only, and this description is notmeant to limit the scope of the invention in any manner whatsoever.

When the novel excipient of the invention utilizes a colloidal silicondioxide, it has been found that the resultant excipient productsurprisingly provides a compressibility which is substantially improvedin preferred embodiments even in comparison to the compressibility ofnormal "off-the-shelf" commercially available microcrystalline celluloseused in direct compression techniques.

In other embodiments of the present invention, it has been discoveredthat the compressibility of microcrystalline cellulose which is wetgranulated is significantly improved by a wider range of silicon dioxideproducts. Thus, in embodiments of the present invention where animprovement in overall compressibility of the microcrystalline cellulose(whether utilized in wet granulation or dry granulation) is notimportant, and the microcrystalline cellulose product is to be subjectedto wet granulation, it has been discovered that the surface area of thesilicon dioxide can be as low as about 50 m² /gm and the average primaryparticle diameter can be as large as about 100 μm. Such silicon dioxideproducts are also deemed to be encompassed within the scope of theinvention.

The coprocessed product consists of microcrystalline cellulose andsilicon dioxide in intimate association with each other. Magnificationsof the resultant particles indicate that the silicon dioxide isintegrated with, or partially coats, the surfaces of themicrocrystalline cellulose particles. When the amount of silicon dioxideincluded in the excipient is greater than about 20% by weight relativeto the microcrystalline cellulose, the silicon dioxide appears tosubstantially coat the surfaces of the microcrystalline celluloseparticles. The exact relationship of the two ingredients of theexcipients after coprocessing is not presently understood; however, forpurposes of description the coprocessed particles are described hereinas including an agglomerate of microcrystalline cellulose and silicondioxide in intimate association with each other. The coprocessedparticles are not necessarily uniform or homogeneous. Rather, undermagnification, e.g., scanning electron microscope at 500×, the silicondioxide at the preferred percent inclusion appears to be an"edge-coating".

Depending upon the amount and type of drying, the concentration of themicrocrystalline cellulose and silicon dioxide in the suspension, thenovel compressible particles will have different particle sizes,densities, pH, moisture content, etc.

The particulate coprocessed product of this aspect of the presentinvention possesses desirable performance attributes that are notpresent when the combination of microcrystalline cellulose and silicondioxide are combined as a dry mixture. It is believed that thebeneficial result obtained by the combination of these two materials isdue to the fact that the two materials are intimately associated witheach other.

One skilled in the art will appreciate that other classes of compoundshaving size, surface area, and other similar physical characteristics tosilicon dioxide may be useful in physically forming a barrier which mayreduce the surface-to-surface interactions (including hydrogen-bonding)between cellulose surfaces. Such materials include (but are not limitedto) non-silicon metal oxides, preferably colloidal. Such obviousmodifications of the present invention are deemed to be within thecontemplated scope of the appended claims.

In other preferred embodiments of the invention, the compressibilityaugmenting agent is a material which inhibits interactions betweenadjacent cellulose surfaces, for example, via the creation of ahydrophobic boundary or barrier at cellulose surfaces. As previouslymentioned, compressibility augmenting agents which inhibitsurface-to-surface interactions between surfaces of the microcrystallinecellulose include any material which has the ability, via a portion ofthe molecule, to bind or interact with the surface of themicrocrystalline cellulose and at the same time, via another portion ofthe molecule, to inhibit the attraction of the cellulose surfaces, e.g.,via a hydrophobic portion or "tail". Suitable compressibility augmentingagents will have an HLB value of at least 10, preferably at least about15, and more preferably from about 15 to about 40 or greater.Compressibility augmenting agents having an HLB value from about 30 toabout 40 or greater is most preferred.

Surfactants which may be used in the present invention as acompressibility augmenting agent generally include allpharmaceutically-acceptable surfactants, with the proviso that thesurfactant have an HLB value of at least 10, and preferably at leastabout 15.

In certain preferred embodiments, the HLB value of the surfactant isfrom about 15 to 50, and in further embodiments is most preferably fromabout 15.6 to about 40. Suitable pharmaceutically-acceptable anionicsurfactants include, for example, those containing carboxylate,sulfonate, and sulfate ions. Those containing carboxylate ions aresometimes referred to as soaps and are generally prepared bysaponification of natural fatty acid glycerides in alkaline solutions.The most common cations associated with these surfactants are sodium,potassium, ammonium and triethanolamine. The chain length of the fattyacids range from 12 to 18. Although a large number of alkyl sulfates areavailable as surfactants, one particularly preferred surfactant issodium lauryl sulfate, which has an HLB value of about 40.

In the pharmaceutical arts, sodium lauryl sulfate has been used as anemulsifying agent in amounts of up to about 0.1% by weight of theformulation. However, surfactants such as sodium lauryl sulfate havebeen included in coprocessed microcrystalline cellulose compositions.Moreover, surfactants have been used in the amounts described herein toimprove the compressibility of microcrystalline cellulose especially inwet granulations. Sodium lauryl sulfate is a water-soluble salt,produced as a white or cream powder, crystals, or flakes and is used asa wetting agent and detergent. Also known as dodecyl sodium sulfate,sodium lauryl sulfate is actually a mixture of sodium alkyl sulfatesconsisting chiefly of sodium lauryl sulfate. Sodium lauryl sulfate isalso known as sulfuric acid monododecyl ester sodium salt. Furthermore,sodium lauryl sulfate is readily available from commercial sources suchas Sigma or Aldrich in both solid form and as a solution. The solubilityof sodium lauryl sulfate is about 1 gm per 10 ml/water. The fatty acidsof coconut oil, consisting chiefly of lauric acid, are catalyticallyhydrogenated to form the corresponding alcohols. The alcohols are thenesterified with sulfuric acid (sulfated) and the resulting mixture ofalkyl bisulfates (alkyl sulfuric acids) is converted into sodium saltsby reacting with alkali under controlled conditions of pH.

Alternative anionic surfactants include docusate salts such as thesodium salt thereof. Other suitable anionic surfactants include, withoutlimitation, alkyl carboxylates, acyl lactylates, alkyl ethercarboxylates, N-acyl sarcosinates, polyvalent alkyl carbonates, N-acylglutamates, fatty acid, polypeptide condensates and sulfuric acidesters.

In other aspects of the invention amphoteric (amphipathic/amphiphilicsurfactants), non-ionic surfactants and/or cationic surfactants areincluded in the coprocessed compositions of the invention. Suitablepharmaceutically-acceptable non-ionic surfactants such as, for example,polyoxyethylene compounds, lecithin, ethoxylated alcohols, ethoxylatedesters, ethoxylated amides, polyoxypropylene compounds, propoxylatedalcohols, ethoxylated/propoxylated block polymers, propoxylated esters,alkanolamides, amine oxides, fatty acid esters of polyhydric alcohols,ethylene glycol esters, diethylene glycol esters, propylene glycolesters, glycerol esters, polyglycerol fatty acid esters, SPAN's (e.g.,sorbitan esters), TWEEN's (i.e., sucrose esters), glucose (dextrose)esters and simethicone. The HLB for one acceptable non-ionic surfactant,polysorbate 40, is about 15.6.

Other suitable pharmaceutically-acceptable surfactants include acacia,benzalkonium chloride, cholesterol, emulsifying wax, glycerolmonostearate, lanolin alcohols, lecithin, poloxamer, polyoxyethylene,and castor oil derivatives.

Those skilled in the art will further appreciate that the name and/ormethod of preparation of the surfactant utilized in the presentinvention is not determinative of the usefulness of the product. Rather,as previously mentioned, it has been surprisingly discovered that it isthe physical characteristics of surfactants, especially those of theanionic class such as sodium lauryl sulfate, which are critical. Inparticular, it has been discovered that when an anionic surfactant suchas sodium lauryl sulfate is coprocessed with microcrystalline cellulosein the amounts described herein, improved microcrystalline celluloseproducts of the invention result.

When the novel excipient of the invention utilizes an anionicsurfactant, it has been found that the resultant excipient productsurprisingly provides a compressibility which is substantially improvedin preferred embodiments even in comparison to the compressibility ofnormal "off-the-shelf" commercially available microcrystalline celluloseused in direct compression techniques. In other embodiments of thepresent invention, it has been discovered that the compressibility ofmicrocrystalline cellulose which is wet granulated is significantlyimproved by coprocessing the microcrystalline cellulose with an anionicsurfactant such as sodium lauryl sulfate.

Since microcrystalline cellulose is substantially water insoluble, theparticle size of this ingredient in the well-dispersed aqueous slurry isdirectly related to its particle size as it was introduced into theaqueous solution. Most surfactants, on the other hand, tend to be watersoluble. Sodium lauryl sulfate, for example, is relatively soluble inwater (1 g/10 ml) and, therefore, dissolves in the aqueous slurry. Itshould be understood, however, that the coprocessed products of thepresent invention are not solely limited to those which contain adissolved surfactant. The contemplated compositions can also be preparedfrom slurries which contain a dispersion of the surfactant as well asthe microcrystalline cellulose.

Highly polar molecules having the requisite HLB value range set forthabove may also be utilized as the compressibility augmenting agent. Suchhighly polar molecules include certain dyes, particular those which maybe capable of binding to the cellulose surface while thereafter creatinga relatively hydrophobic environment due to the presence of ahydrophobic portion of the molecule (e.g., a hydrophobic tail) which"points away" from the cellulose surface and discourages hydrophilicsurface-to-surface cellulose interactions, such as hydrogen-bonding.Preferably, the dye is one which is pharmaceutically acceptable forinclusion in solid dosage forms.

Examples of suitable dyes include Congo Red (chemical name:3,3'-[[1,1'Biphenyl]-4,4'-diylbis-(azo)]bis[4-amino-1-naphthalenesulfonicacid] disodium salt; FD&C Red No. 40 (also known as "Allura Red")(chemical name: Disodium salt of6-hydroxy-5[(2-methyl-4-sulfophenyl)azo]-2-naphthalenesulfonic acid);FD&C Yellow No. 5 (common name: tartrazine) (chemical name:5-oxo-1-(p-sulfophenyl)-4-[(p-sulfophenyl)azo]-2-pyrazoline-3-carboxylicacid, trisodium salt); FD&C Yellow No. 6 (common name: Sunset YellowFCF) (chemical name: Disodium salt of1-p-sulphophenylazo-2-naphthol-6-sulfonic acid); Ponceau 4R (chemicalname:Trisodium-2-hydroxy-1-(4-sulfonato-1-naphthylazo)naphthalene-6,8-disulfonate);Brown HT (chemical name: Disodium4,4'-(2,4-dihydroxy-5-hydroxymethyl-3,3-phenylenebisazo)di(napthalene-1-sulfonate)); Brilliant Black BN (Chemical name:Tetrasodium4-acetamido-5-hyroxy-6-[7-sulfonato-4-(4-sulfonatophenylazo)-1-naphthylazo]naphthalene-1,7-disulfonate);Carmoisine (chemical name: Disodium4-hydroxy-3-(4-sulfanato-1-naphythylazo) Naphthalene-1-sulfonate);Amaranth (chemical name: Trisodium2-hydroxy-1-(4-sulfonato-1-naphthylazo)naphthalene-3,6-disulfonate); andmixtures thereof.

Other highly polar molecules having the requisite HLB value range setforth above which may be utilized as the compressibility augmentingagent include the active agents themselves. For example, it iswell-known to those skilled in the art that certain classes ofpharmaceuticals, such as anti-pyschotic drugs, are highly polar innature and may be utilized as a compressibility augmenting agent inaccordance with this invention.

One skilled in the art will appreciate that other classes of highlypolar compounds may be useful in reducing the surface-to-surfaceinteractions (including hydrogen-bonding) between cellulose surfaces.Such obvious modifications of the present invention are deemed to bewithin the contemplated scope of the appended claims.

It is preferred in the present invention that the microcrystallinecellulose and compressibility augmenting agent are coprocessed,resulting in an intimate association of these ingredients, rather thanbeing combined, e.g., as a dry mixture. In preferred embodiments of thepresent invention, an aqueous slurry of the microcrystalline cellulose,the compressibility augmenting agent(s) and other optional ingredientsis prepared in order to obtain (after a drying step) agglomeratedparticles wherein these components are intimately associated. Theaqueous slurry of the microcrystalline cellulose and compressibilityaugmenting agent are introduced into the spray dryer as a single aqueousmedium. However, it is possible to separately introduce each ingredientinto separate aqueous medium which are then combined. Other proceduresfor combining these materials with or without other optional ingredientsknown to those skilled in the art are deemed to be equivalent to thespray-drying technique described above, and are further deemed to beencompassed by the appended claims.

In preferred embodiments of the present invention, the coprocessing ofthe microcrystalline cellulose and compressibility augmenting agent isaccomplished by forming a well-dispersed aqueous slurry ofmicrocrystalline cellulose in which the compressibility augmenting agenthas been dissolved, and thereafter drying the slurry and forming aplurality of microcrystalline cellulose-based excipient particles.Typically, microcrystalline cellulose is first added to an aqueoussolution so that a slurry or suspension containing from about 0.5% toabout 25% microcrystalline cellulose in the form of solids is obtained.Preferably, the slurry or suspension contains from about 15% to 20%microcrystalline cellulose and most preferably from about 17% to about19% microcrystalline cellulose. At this stage, it is optionallydesirable to adjust the pH of the slurry to about neutral with ammoniumhydroxide, sodium hydroxide, and mixtures thereof or the like. Thesuspension is kept under constant agitation for a sufficient time toassure a uniform distribution of the solids prior to being combined withthe compressibility augmenting agent.

For example, silicon dioxide is added to the suspension or slurry inamounts ranging from 0.1% to about 20% by weight, based on the amount ofmicrocrystalline cellulose, amounts from about 0.5% to about 10% arepreferred while amounts of from about 1.25% to about 5% by weight areespecially preferred. There is no appreciable dissolution of eitheringredient (microcrystalline cellulose or silicon dioxide), since bothare relatively water insoluble. The microcrystalline cellulose andsilicon dioxide are well-dispersed in the slurry or suspension prior todrying and forming the novel particles.

On the other hand, the surfactant is added to the suspension or slurryin amounts ranging from about 0.1% to about 20% by weight, preferablyfrom about 0.1 to about 5% by weight, based on the amount ofmicrocrystalline cellulose, and in certain embodiments preferably fromabout 0.15% to about 0.4%, by weight. When the surfactant is sodiumlauryl sulfate, the amount is most preferably from about 0.2 to about0.3%, by weight. The surfactant can be added to the suspension as eithera solid or in solution form. The microcrystalline cellulose is thuswell-dispersed in the slurry or suspension and the surfactant isdissolved therein prior drying and forming the novel particles. It willbe understood that other useful surfactants can be used in like amountsor even greater amounts, i.e. up to 20% by weight or even more. Theusable concentration range for the selected surfactant depends in partupon not only its molecular weight but also its degree of foaming,particularly when present in agitated slurries which will be spray driedto form the desired particulate. Thus, in those aspects of the inventionwhere surfactants other than sodium lauryl sulfate are coprocessed withthe microcrystalline cellulose, it is to be understood that thesurfactant will be present in an amount which enhances thecompressibility of the Microcrystalline cellulose and yet does not havea degree of foaming which would substantially inhibit spray drying.

Other compressibility augmenting agents (including highly polar dyes,highly polar drugs, and other useful materials having a HLB from about15 to about 50) may be included in the aqueous slurry in amounts rangingfrom about 0.1% to about 20%, by weight, and more preferably from about0.5 to about 10%, by weight.

After a uniform mixture of the ingredients is obtained in thesuspension, the suspension is dried to provide a plurality ofmicrocrystalline cellulose-based excipient particles having enhancedcompressibility (e.g., dried in a manner which inhibitsquasi-hornification).

In the (preferred) spray-drying process, the aqueous dispersion ofmicrocrystalline cellulose and surfactant is brought together with asufficient volume of hot air to produce evaporation and drying of theliquid droplets. The highly dispersed slurry of microcrystallinecellulose and surfactant is pumpable and capable of being atomized. Itis sprayed into a current of warm filtered air, which supplies the heatfor evaporation and conveys a dried product to a collecting device. Theair is then exhausted with the removed moisture. The resultantspray-dried powder particles are approximately spherical in shape andare relatively uniform in size, thereby possessing excellentflowability. The coprocessed product consists of microcrystallinecellulose and surfactant in intimate association with each other. Theexact relationship of the two ingredients of the excipients aftercoprocessing is not presently understood; however, for purposes ofdescription the coprocessed particles are described herein as includingan agglomerate of microcrystalline cellulose and surfactant in intimateassociation with each other. By "intimate associate", it is meant thatthe surfactant has in some manner been integrated with themicrocrystalline cellulose particles, e.g., via a partial coating of themicrocrystalline particles, as opposed to a chemical interaction of thetwo ingredients. The term "intimate association" is therefore deemed forpurposes of the present description as being synonymous with"integrated" or "united". The coprocessed particles are not necessarilyuniform or homogeneous.

It is preferred that the suspension be dried using spray-dryingtechniques, as they are known in the art. Other drying techniques,however, such as flash drying, ring drying, micron drying, tray drying,vacuum drying, radio-frequency drying, and possibly microwave drying,may also be used, although spray drying is preferred.

Depending upon the amount and type of drying, the concentration of themicrocrystalline cellulose and compressibility augmenting agent in thesuspension, the novel compressible particles will have differentparticle sizes, densities, pH, moisture content, etc.

The particulate coprocessed product of the present invention possessesdesirable performance attributes that are not present when thecombination of microcrystalline cellulose and compressibility augmentingagent are combined as a dry mixture. It is believed that the beneficialresult obtained by the combination of these two materials is due to thefact that the two materials are intimately associated with each other.It has also been found that intimate association of Microcrystallinecellulose and other detergent-like materials such as simethicone, evenwhen they are dissolved/dispersed in the aqueous solutions which formthe Microcrystalline cellulose slurry, fail to provide Microcrystallinecellulose with enhanced compressibility.

The average particle size of the agglomerated microcrystalline celluloseexcipient of the present invention ranges from about 10 microns to about1000 microns. Particle sizes of about 10-500 microns are preferred,particle sizes of about 30-250 microns are more preferred and particlesizes of about 40-200 microns are most preferred. It will be appreciatedby those of ordinary skill in the art that the drying of the aqueoussuspension results in a random size distribution of the novel excipientparticles being produced. For example, if spray drying techniques areused, droplet size, temperatures, agitation, dispersion, air flow,atomizer wheel speed, etc. will effect final particle size. Furthermore,it is within the scope of the invention to sort or mechanically alterthe dried particles according to ranges of particle sizes depending uponend uses. The particle size of the integrated excipient is not narrowlycritical, the important parameter being that the average size of theparticle must permit the formation of a directly compressible excipientwhich forms pharmaceutically acceptable tablets.

The novel agglomerated microcrystalline cellulose excipient has a bulk(loose) density ranging from about 0.2 g/ml to about 0.6 g/ml, and mostpreferably from about 0.22 g/ml to about 0.55 g/ml. The novel excipienthas a tapped density ranging from about 0.20 g/ml to about 0.70 g/ml,and most preferably from about 0.35 g/ml to about 0.60 g/ml. The pH ofthe particles is most preferably about neutral, although granulateshaving a pH of from about 3.0 to about 8.5 are possible. The moisturecontent of the excipient particles will broadly range from about 0.5% toabout 15%, preferably from about 2.5% to about 6%, and most preferablyfrom about 3.0% to about 5% by weight.

The angle of repose is a measurement used to determine the flowcharacteristics of a powder. The angle of repose is subject toexperiment and experimenter, but in a comparative test, the novelexcipient is superior.

The novel agglomerated microcrystalline cellulose excipient of theinvention is free-flowing and directly compressible. Accordingly, theexcipient may be mixed in the desired proportion with an active agentand optional lubricant (dry granulation), and then directly compressedinto solid dosage forms. In preferred embodiments of the presentinvention wherein the surfactant is sodium lauryl sulfate, the novelexcipient represents an augmented microcrystalline cellulose havingimproved compressibility as compared to standard commercially availablegrades of microcrystalline cellulose.

Alternatively, all or part of the excipient may be subjected to a wetgranulation with the active ingredient. A representative wet granulationincludes loading the novel excipient particles into a suitablegranulator, such as those available from Baker-Perkins, and granulatingthe particles together with the active ingredient, preferably using anaqueous granulating liquid. The granulating liquid is added to themixture with stirring until the powdery mass has the consistency of dampsnow and then wet screened through a desired mesh screen, for example,having a mesh from about 12 to about 16. The screened granulate is thendried, using standard drying apparatus such as a convection oven beforeundergoing a final screening. Additional dry screening of this materialis possible, such as by using screens of from about 40 to about 200mesh. Those materials flowing through 40 and 60 mesh screens may befurther ground prior to ultimate tablet formulation. The thus obtainedgranulate containing the novel excipient is now capable of undergoingtableting or otherwise placed into a unit dosage form.

In certain preferred embodiments, a portion of the total amount of thenovel excipient is wet granulated with the active ingredient, andthereafter the additional portion of the novel excipient is added to thegranulate. In yet other embodiments, the additional portion of the novelexcipient to be added to the excipient/active ingredient granulate maybe substituted with conventional microcrystalline cellulose, or otherexcipients commonly used by those skilled in the art, depending ofcourse upon the requirements of the particular formulation.

By virtue of the novel excipient of the present invention, the amount ofthe novel excipient compared to the amount of microcrystalline cellulosewhich must be used in a wet granulation technique to obtain anacceptable solid dosage form is substantially reduced.

In other embodiments of the invention, a further material is added tothe aqueous slurry of microcrystalline cellulose and compressibilityaugmenting. Such additional materials include silicon dioxides,non-silicon metal oxides, starches, starch derivatives, surfactants,polyalkylene oxides, cellulose ethers, celluloses esters, mixturesthereof, and the like. Specific further materials which may be includedin the aqueous slurry (and consequently in the resultant agglomeratedmicrocrystalline cellulose excipient) are aluminum oxide, stearic acid,kaolin, polydimethylsiloxane, silica gel, titanium dioxide, diatomaceousearth, corn starch, high amylose corn starch, high amylopectin cornstarch, sodium starch glycolate, hydroxylated starch, modified potatostarch, mixtures thereof, and the like. These additives may be includedin desired amounts which will be apparent to those skilled in the art.

In addition to one or more active ingredients, additionalpharmaceutically acceptable excipients (in the case of pharmaceuticals)or other additives known to those skilled in the art (fornon-pharmaceutical applications) can be added to the novel excipientprior to preparation of the final product. For example, if desired, anygenerally accepted soluble or insoluble inert pharmaceutical filler(diluent) material can be included in the final product (e.g., a soliddosage form). Preferably, the inert pharmaceutical filler comprises amonosaccharide, a disaccharide, a polyhydric alcohol, inorganicphosphates, sulfates or carbonates, and/or mixtures thereof. Examples ofsuitable inert pharmaceutical fillers include sucrose, dextrose,lactose, xylitol, fructose, sorbitol, calcium phosphate, calciumsulfate, calcium carbonate, "off-the-shelf" microcrystalline cellulose,mixtures thereof, and the like.

An effective amount of any generally accepted pharmaceutical lubricant,including the calcium or magnesium soaps may optionally be added to thenovel excipient at the time the medicament is added, or in any eventprior to compression into a solid dosage form. The lubricant maycomprise, for example, magnesium stearate in any amount of about 0.5-3%by weight of the solid dosage form. In embodiments where a surfactant isincluded as part or all of the compressibility augmenting agent, anadditional inclusion lubricant may not be necessary.

The complete mixture, in an amount sufficient to make a uniform batch oftablets, may then subjected to tableting in a conventional productionscale tableting machine at normal compression pressures for thatmachine, e.g., about 1500-10,000 lbs/sq in. The mixture should not becompressed to such a degree that there is subsequent difficulty in itshydration when exposed to gastric fluid.

The average tablet size for round tablets is preferably about 50 mg to500 mg and for capsule-shaped tablets about 200 mg to 2000 mg. However,other formulations prepared in accordance with the present invention maybe suitably shaped for other uses or locations, such as other bodycavities, e.g., periodontal pockets, surgical wounds, vaginally. It iscontemplated that for certain uses, e.g., antacid tablets, vaginaltablets and possibly implants, that the tablet will be larger.

The active agent(s) which may be incorporated with the novel excipientdescribed herein into solid dosage forms invention include systemicallyactive therapeutic agents, locally active therapeutic agents,disinfecting agents, chemical impregnants, cleansing agents, deodorants,fragrances, dyes, animal repellents, insect repellents, fertilizingagents, pesticides, herbicides, fungicides, and plant growth stimulants,and the like.

A wide variety of therapeutically active agents can be used inconjunction with the present invention. The therapeutically activeagents (e.g. pharmaceutical agents) which may be used in thecompositions of the present invention include both water soluble andwater insoluble drugs. Examples of such therapeutically active agentsinclude antihistamines (e.g., dimenhydrinate, diphenhydramine,chlorpheniramine and dexchlorpheniramine maleate), analgesics (e.g.,aspirin, codeine, morphine, dihydromorphone, oxycodone, etc.),non-steroidal anti-inflammatory agents (e.g., naproxyn, diclofenac,indomethacin, ibuprofen, sulindac), anti-emetics (e.g., metoclopramide),anti-epileptics (e.g., phenytoin, meprobamate and nitrazepam),vasodilators (e.g., nifedipine, papaverine, diltiazem and nicardirine),anti-tussive agents and expectorants (e.g., codeine phosphate),anti-asthmatics (e.g. theophylline), antacids, anti-spasmodics (e.g.atropine, scopolamine), antidiabetics (e.g., insulin), diuretics (e.g.,ethacrynic acid, bendrofluazide), anti-hypotensives (e.g., propranolol,clonidine), antihypertensives (e.g., clonidine, methyldopa),bronchodilators (e.g., albuterol), steroids (e.g., hydrocortisone,triamcinolone, prednisone), antibiotics (e.g., tetracycline),antihemorrhoidals, hypnotics, psychotropics, antidiarrheals, mucolytics,sedatives, decongestants, laxatives, vitamins, stimulants (includingappetite suppressants such as phenylpropanolamine). The above list isnot meant to be exclusive.

A wide variety of locally active agents can be used in conjunction withthe novel excipient described herein, and include both water soluble andwater insoluble agents. The locally active agent(s) which may beincluded in the controlled release formulation of the present inventionis intended to exert its effect in the environment of use, e.g., theoral cavity, although in some instances the active agent may also havesystemic activity via absorption into the blood via the surroundingmucosa.

The locally active agent(s) include antifungal agents (e.g.,amphotericin B, clotrimazole, nystatin, ketoconazole, miconazol, etc.),antibiotic agents (penicillins, cephalosporins, erythromycin,tetracycline, aminoglycosides, etc.), antiviral agents (e.g, acyclovir,idoxuridine, etc.), breath fresheners (e.g. chlorophyll), antitussiveagents (e.g., dextromethorphan hydrochloride), anti-cariogenic compounds(e.g., metallic salts of fluoride, sodium monofluorophosphate, stannousfluoride, amine fluorides), analgesic agents (e.g., methylsalicylate,salicylic acid, etc.), local anesthetics (e.g., benzocaine), oralantiseptics (e.g., chlorhexidine and salts thereof, hexylresorcinol,dequalinium chloride, cetylpyridinium chloride), anti-inflammatoryagents (e.g., dexamethasone, betamethasone, prednisone, prednisolone,triamcinolone, hydrocortisone, etc.), hormonal agents (oestriol),antiplaque agents (e.g, chlorhexidine and salts thereof, octenidine, andmixtures of thymol, menthol, methysalicylate, eucalyptol), acidityreducing agents (e.g., buffering agents such as potassium phosphatedibasic, calcium carbonate, sodium bicarbonate, sodium and potassiumhydroxide, etc.), and tooth desensitizers (e.g., potassium nitrate).This list is not meant to be exclusive. The solid formulations of theinvention may also include other locally active agents, such asflavorants and sweeteners. Generally any flavoring or food additive suchas those described in Chemicals Used in Food Processing, pub 1274 by theNational Academy of Sciences, pages 63-258 may be used. Generally, thefinal product may include from about 0.1% to about 5% by weightflavorant.

The tablets of the present invention may also contain effective amountsof coloring agents, (e.g., titanium dioxide, F.D. & C. and D. & C. dyes;see the Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 5, pp.857-884, hereby incorporated by reference), stabilizers, binders, odorcontrolling agents, and preservatives.

Alternatively, the novel excipient can be utilized in other applicationswherein it is not compressed. For example, the granulate can be admixedwith an active ingredient and the mixture then filled into capsules. Thegranulate can further be molded into shapes other than those typicallyassociated with tablets. For example, the granulate together with activeingredient can be molded to "fit" into a particular area in anenvironment of use (e.g., an implant). All such uses would becontemplated by those skilled in the art and are deemed to beencompassed within the scope of the appended claims.

In further embodiments of the invention, more than one compressibilityaugmenting agent is used. Thus, for example, it is possible to use twoor more agents which act as physical barriers (e.g., physicallyrestricting the proximity of the interface between adjacent cellulosesurfaces); or to use two or more agents which inhibit interactionsbetween adjacent cellulose surfaces, for example, via the creation of ahydrophobic boundary at cellulose surfaces (e.g., surfactants having therequisite HLB value, and/or highly polar materials such as thepreviously mentioned dyes).

In certain preferred embodiments, two or more compressibility enhancingagents are used which provide an effect by different mechanisms, such asone agent which acts as a physical barrier (such as colloidal silicondioxide), and another agent which inhibit interactions between adjacentcellulose surfaces (for example, sodium lauryl sulfate). In suchembodiments, it is preferred that both agents are incorporated into theaqueous slurry and dried (e.g., via spray drying) to form agglomeratedparticles in which the microcrystalline cellulose, colloidal silicondioxide and sodium lauryl sulfate are in intimate association. Suchpreferred embodiments are capable of providing a synergisticallyimproved microcrystalline cellulose excipient which has propertiesdescribed above which are at least as good, and preferably improved, ascompared to the properties of the novel microcrystalline celluloseexcipients which include only one class of these compressibilityaugmenting agents.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate various aspects of the presentinvention. They are not to be construed to limit the claims in anymanner whatsoever.

The examples set forth the preparation of various microcrystallinecellulose/silicon dioxide compositions. Tablets were prepared using eachof the compositions and each of tablet preparations was tested fortensile strength.

Examples 1-3 Preparation of Coprocessed Microcrystalline Cellulose-SiO₂Compositions and Granulations Thereof Example 1 MCC-SiO₂ Product-5% w/wSiO₂

A. EXCIPIENT PARTICLES

In this example, about 6.2 kilograms of microcrystalline cellulose(MCC), (Mendell Co., Inc. Patterson, N.Y.) in the form of a wet cake wascombined with 5.2 kilograms of water in a mix tank to form a slurrycontaining about 15% solids. The pH was adjusted to about neutral withabout 3 ml of ammonium hydroxide. The slurry was allowed to mix forabout 15 minutes before being combined with 5% w/w silicon dioxide(SiO₂), 200 m² /g (CaboSil, PTG grade, available from Cabot Corp.,Tuscola, Ill.) After allowing the materials to become intimatelycombined, the slurry was spray dried using a Niro Production Minor(Niro, Columbia, Md.), inlet temperature-215° C., outlettemperature-125° C., atomizer wheel speed 22,300 rpm, to providemicrocrystalline cellulose-SiO₂ having an average particle size of 40-60microns.

B. GRANULATION OF EXCIPIENT PARTICLES

The microcrystalline cellulose-SiO₂ particles obtained as a result ofstep 1 A. were wet granulated in a Baker-Perkins 10 liter high-sheergranulator for 3 minutes using water as the granulating fluid. Theresultant product was wet screened through a 12 mesh screen, tray driedin a convection oven for about 2-3 hours until a moisture content ofless than 5% was obtained, dry screened and sieved to obtain an averageparticle size of from about 55 to about 70 microns.

Example 2 MCC-SiO₂ Product-20% w/w SiO₂

The processes of Example 1A and B were repeated except that 20% w/wsilicon dioxide was used to form the product.

Example 3 MCC-SiO₂ Product-2% w/w SiO₂

In this example, the processes of Example 1A and B were repeated exceptthat 2% w/w silicon dioxide was used to form the product.

Example 4 Dry Blend Mix of MCC and SiO₂ (5% w/w)-Comparative

As a control, EMCOCEL® grade 50 M microcrystalline cellulose (MendellCo., Inc.) and 5% w/w silicon dioxide, 200 m² /g (CaboSil, PTG grade)were dry blended. No spray drying or other treatment of the mixture wasundertaken. The method of Example 1B, however, was repeated.

Example 5 Processed MCC without SiO2

As a second control, the process described in Example 1B was repeatedexcept that no SiO₂ was added.

Example 6

In this example, batches of compressed tablets were prepared using eachof the products obtained as a result of Examples 1-5. The tablets wereprepared using a Korsch tablet press having a punch size of 3/8" and anaim weight of about 245 mg. The granulations were included in fiveseparate tabletting runs using compression forces of 6, 12, 18, 24 and30 kN respectively. Ten tablets from each run were weighed, measured fordiameter and tested for thickness and hardness on the Erweka TBH 30tablet hardness tester to determine the compressibility of themicrocrystalline cellulose as measured by tensile strength. The resultsof the analysis are graphically illustrated in FIG. 1 as a comparison oftensile strength versus compression force.

As can be seen from the graph, substantial benefits are obtained bycoprocessing microcrystalline cellulose with SiO₂. The tablets preparedusing the products of comparative examples 4 and 5 demonstrated poortensile strength. The novel excipient is superior and demonstratesapproximately the same relative improvement across the entire range ofcompression forces. Furthermore, the graph also illustrates that tabletsprepared with a mere dry admixture of microcrystalline cellulose andSiO₂ (example 4 formulation) failed to demonstrate acceptable tensilestrengths. Thus, the coprocessed microcrystalline cellulose-SiO₂described herein provides significant retention of microcrystallinecellulose compressibility.

Examples 7-12

In these examples, compressed tablet products containing 70% by weightmicrocrystalline cellulose and 30% acetaminophen (APAP herein) wereprepared. The products of examples 7-9 were controls and preparedwithout the coprocessed microcrystalline cellulose-SiO₂ of the presentinvention. The products of examples 10-12, on the other hand, included70% by weight of the novel coprocessed microcrystalline cellulose-SiO₂and 30% APAP. Details concerning the preparation of each granulationproduct is set forth below. A graphical comparison of the tensilestrength versus compression force for each tabletted product is providedin FIG. 2.

Example 7 Intragranulation and Extragranulation of APAP withMicrocrystalline Cellulose

In this example, tablets were prepared using off-the-shelfmicrocrystalline cellulose (EMCOCEL® 50 M) according to the followingformula:

    ______________________________________                                        INGREDIENTS      WEIGHT (GRAMS)                                               ______________________________________                                        Microcrystalline cellulose                                                                     267.9                                                        APAP             114.8                                                        Deionized water  165.8                                                        ______________________________________                                    

One half of the microcrystalline cellulose was added to a Baker-Perkins10 liter blender and combined with all of the APAP. The blender impellerwas adjusted to 200 rpm and the chopper was set at 1000 rpm. After oneminute, the water was added over 90 seconds using a rinse bottle.Thereafter, mixing was continued for an additional 90 seconds. Thegranulation was removed from the blender, wet screened through a 12screen mesh and dried in a convection oven for 2-3 hours at 60° C. untila moisture content of less than 5% was obtained. The granulation wasthen dry screened through a 16 mesh screen before being blended for 10minutes with the remaining portion of the microcrystalline cellulose ina two quart V-blender. The granulation was removed from the blender andtabletted in accordance with the method described below.

Tablet Strength Testing

In order to prepare tablets for the formulations of examples 7, 8, 10and 11, the following procedure was used:

the wet granulation products were weighed and mixed in a 2 quartV-blender for 5 minutes with 0.2% Pruv™ (sodium stearyl fumarate,available from Mendell Co., Inc.).

Five separate tabletting runs were undertaken with compression forces of5, 10, 15, 20 and 25 kN respectively using a Korsch tablet press havinga punch size of 3/8" and an aim weight of about 245 mg. Ten tablets fromeach compression force were selected and used in the experiment setforth in Example 13.

Example 8 Wet Granulation of APAP With MCC

In this example, only wet granulation or the intragranulation step asdescribed above was undertaken. The formulation was prepared accordingto the following formula using off-the-shelf EMCOCEL® 50 Mmicrocrystalline cellulose:

    ______________________________________                                        INGREDIENTS      WEIGHT (GRAMS)                                               ______________________________________                                        Microcrystalline cellulose                                                                     178.6                                                        APAP             76.5                                                         Deionized water  170.1                                                        ______________________________________                                    

The microcrystalline cellulose was added to a Baker-Perkins 10 literblender and combined with the APAP. The blender impeller was adjusted to200 rpm and the chopper was set at 1000 rpm. After one minute, the waterwas added over 90 seconds using a rinse bottle. Thereafter, mixing wascontinued for an additional 90 seconds. The granulation was removed fromthe blender, wet screened through a 12 screen mesh and then dried in aconvection oven at 60° C. for 2-3 hours, until a moisture content ofless than 5% was achieved. The granulation was then dry screened througha 16 mesh screen and tabletted in accordance with the method describedin example 7.

Example 9 Direct Compression Formulation of APAP With MCC

A direct compression formulation for tablets was prepared to contain 70%off-the-shelf EMCOCEL® 50 M microcrystalline cellulose and 30% APAP byweight. The tablets were prepared according to the following formula:

    ______________________________________                                        INGREDIENTS      WEIGHT (GRAMS)                                               ______________________________________                                        Microcrystalline cellulose                                                                     175.0                                                        APAP             74.5                                                         PRUV             0.5                                                          ______________________________________                                    

The microcrystalline cellulose and APAP were combined in a V-blender andmixed for 15 minutes. Thereafter, the Pruv® (stearyl fumarate,commercially available from Edward Mendell Co., Inc.) was added andmixing was continued for another 5 minutes. The granulation was removedand five separate tabletting runs were undertaken using compressionforces of 5, 10, 15, 20 and 25 kN respectively on a Korsch tablet press.The tablet press had a punch size of 3/8" and an aim weight of about 245mg. Ten tablets from each compression force were used in the experimentset forth in Example 13.

Example 10 Wet Granulation of APAP With Coprocessed MicrocrystallineCellulose-SiO₂ (5% w/w)

In this example, tablets were prepared by wet granulation with thecoprocessed microcrystalline cellulose (5% w/w SiO₂) of Example 1A. Thetablet granulation was prepared according to the following formula:

    ______________________________________                                        INGREDIENTS       WEIGHT (GRAMS)                                              ______________________________________                                        Microcrystalline Cellulose-SiO.sub.2                                                            178.6                                                       APAP              76.5                                                        Deionized water   170.1                                                       ______________________________________                                    

The microcrystalline cellulose-SiO₂ was added to a Baker-Perkins 10liter blender and combined with the APAP. The blender impeller wasadjusted to 200 rpm and the chopper was set at 1000 rpm. After oneminute, the water was added over 90 seconds using a rinse bottle.Thereafter, mixing was continued for an additional 90 seconds. Thegranulation was removed from the blender, wet screened through a 12screen mesh and then dried in a convection oven for 2-3 hours at 60° C.until a moisture content of less than 5% was achieved. The granulationwas then dry screened through a 16 mesh screen and tabletted accordingto the method set forth in Example 7.

Example 11

Intra- and Extragranulation of APAP with Microcrystalline Cellulose-SiO₂(5% w/w)

    ______________________________________                                        INGREDIENTS       WEIGHT (GRAMS)                                              ______________________________________                                        Microcrystalline Cellulose-SiO.sub.2                                                            267.9                                                       APAP              114.8                                                       Deionized water   165.8                                                       ______________________________________                                    

One half of the coprocessed Microcrystalline cellulose-SiO₂ (prepared asin Example 1A) was added to a Baker-Perkins 10 liter blender andcombined with all of the APAP. The blender impeller was adjusted to 200rpm and the chopper was set at 1000 rpm. After one minute, the water wasadded over 90 seconds using a rinse bottle. Thereafter, mixing wascontinued for an additional 90 seconds. The granulation was removed fromthe blender, wet screened through a 12 screen mesh and then dried in aconvection oven for 2-3 hours at 60° C. until a moisture content of lessthan 5% was achieved. The granulation was then dry screened through a 16mesh screen before being blended for 10 minutes with the remainingportion of the coprocessed Microcrystalline cellulose-SiO₂ in a 2 quartV-blender, removed from the blender, and tabletted according to themethod of Example 7.

Example 12 Direct Compression Formulation of APAP With MicrocrystallineCellulose-SiO₂ (5% w/w)

A direct compression formulation similar to that set forth in example 9was undertaken except that the tablets were prepared to contain thecoprocessed Microcrystalline cellulose-SiO₂ of Example 1A. The tabletgranulation was prepared according to the following formula:

    ______________________________________                                        INGREDIENTS       WEIGHT (GRAMS)                                              ______________________________________                                        Microcrystalline cellulose-SiO.sub.2                                                            175.0                                                       APAP              74.5                                                        PRUV              0.5                                                         ______________________________________                                    

As was the case in example 9, five separate tabletting runs wereundertaken using compression forces of 5, 10, 15, 20 and 25 kNrespectively on a Korsch tablet press, (punch size: 3/8" and aimweight--about 245 mg). Ten tablets from each compression force were usedto carry out the experiment set forth in Example 13.

Example 13 Tablet Strength Testing

Ten tablets from each compression force run for each formulationprepared in Examples 7-12 were weighed, measured for diameter and testedfor thickness and hardness on the Erweka TBH 30 tablet hardness testerto determine the compressibility of the microcrystalline cellulose. Theresults are graphically illustrated in FIG. 2 as a comparison of tensilestrength versus compression force.

Referring now to FIG. 2, it can be seen that compressed tablets madewith the inventive coprocessed Microcrystalline cellulose-SiO₂ haverelatively high tensile strengths when compared to those made withoff-the-shelf Microcrystalline cellulose. The advantages of thecoprocessed Microcrystalline cellulose-SiO₂ are clearly seen in bothdirect compression and wet granulation formulations and especially inwet granulation products.

Examples 14-16 Diatomaceous Earth

In these examples, the coprocessing method described in Example 1A wasrepeated except that diatomaceous earth of about 40 micron particle size(J. T. Baker, Phillipsburg, N.J. was used as the source of SiO₂).

    ______________________________________                                        Example     Diatomaceous Earth (wt %)                                         ______________________________________                                        14          2.0                                                               15          1.0                                                               16          0.5                                                               ______________________________________                                    

The resultant granulates prepared according to Example 1B were tablettedaccording to the same method described in Example 6 and evaluated fortensile strength. The products of inventive Example 3 (Microcrystallinecellulose-SiO₂ 2% w/w) and Example 5 (Microcrystalline cellulose alone)were included in FIG. 3 for comparison purposes.

Referring now to FIG. 3, it can be seen that although the retention ofcompressibility afforded by coprocessing diatomaceous earth is not asgreat as that provided by colloidal SiO₂ having surface areas of about200 m² /g, the coprocessed Microcrystalline cellulose-diatomaceous earthnonetheless demonstrates improved compressibility in wet granulationformulations.

Examples 17-19 Silica Gel SILICA GEL

In these examples, the coprocessing method described in Example 1A wasrepeated using silica gel 200 micron particle size (VWR Corp.,Piscataway, N.J. as the source of SiO₂).

    ______________________________________                                        Example      Silica Gel (wt %)                                                ______________________________________                                        17           1                                                                18           2                                                                19           5                                                                ______________________________________                                    

The resultant granulates prepared according to Example 1B were tablettedaccording to the same method described in Example 6 and evaluated fortensile strength. The products of inventive Example 3 (Microcrystallinecellulose-SiO₂ 2% w/w) and Example 5 (Microcrystalline cellulose alone)were included in FIG. 4 for comparison purposes.

Referring now to FIG. 4, it can be seen that the retention ofcompressibility afforded by coprocessing with silica gel is well belowthat provided by colloidal SiO₂ having surface areas of about 200 m² /g.In fact, Microcrystalline cellulose coprocessed with silica geldemonstrates compressibility properties about the same as off-the-shelfMicrocrystalline cellulose in wet granulation formulations.

Examples 20-22 HS-5 Grade Silicon Dioxide

In these examples, the coprocessing method described in example 1 wasrepeated using HS-5 grade SiO₂ surface area--325 m² /g (Cabot Corp.,Tuscola, Ill.).

    ______________________________________                                        Example      Silica Gel (wt %)                                                ______________________________________                                        20           2                                                                21           1                                                                22           0.5                                                              ______________________________________                                    

The resultant granulates prepared according to Example 1B were tablettedaccording to the same method described in Example 6 and evaluated fortensile strength. The products of inventive Example 3 (Microcrystallinecellulose-SiO₂ 2% w/w) and Example 5 (off-the-shelf Microcrystallinecellulose) were included in FIG. 5 for comparison purposes.

Referring now to FIG. 5, the retention of compressibility afforded bycoprocessing with HS-5 is comparable to that obtained using SiO₂ havingsurface areas of about 200 m² /g.

While there have been described what are presently believed to be thepreferred embodiments of the invention, those skilled in the art willrealize that changes and modifications may be made thereto withoutdeparting from the spirit of the invention. It is intended to claim allsuch changes and modifications that fall within the true scope of theinvention.

Examples 23-25 Preparation of Coprocessed Microcrystalline Cellulose-SLSCompositions and Granulations Thereof Example 23 MicrocrystallineCellulose-SLS Product-0.25% w/w SLS

A. EXCIPIENT PARTICLES

In this example, about 6.2 kilograms of microcrystalline cellulose(Microcrystalline cellulose), (Mendell Co., Inc. Patterson, N.Y.) in theform of a wet cake was combined with 5.2 kilograms of water in a mixtank to form a slurry containing about 15% solids. The pH was adjustedto about neutral with about 3 ml of ammonium hydroxide. The slurry wasallowed to mix for about 15 minutes before being combined with 0.25% w/wsodium lauryl sulfate (SLS) powder (available from Spectrum Chemical,Gardena, Calif.) After allowing the materials to become intimatelycombined, the slurry was spray dried using a Niro Production Minor(Niro, Columbia, Md.), inlet temperature--215° C., outlettemperature--125° C., atomizer wheel speed 22,300 rpm, to provideMicrocrystalline cellulose-SLS having an average particle size of 40-60microns.

B. GRANULATION OF EXCIPIENT PARTICLES

The Microcrystalline cellulose-SLS particles obtained as a result ofstep 23 A. were wet granulated in a Baker-Perkins 10 liter high-sheergranulator for 3 minutes using water as the granulating fluid. Theresultant product was wet screened through a 12 mesh screen, tray driedin a convection oven for about 2-3 hours until a moisture content ofless than 5% was obtained, dry screened and sieved to obtain an averageparticle size of from about 55 to about 70 microns.

Examples 24-27 Microcrystalline Cellulose-SLS Products

The processes of Example 23A and B were repeated except that 0.5% w/wsodium lauryl sulfate was used to form the product of Example 24; 0.1%w/w SLS was used to form the product of Example 25; 0.2% w/w SLS wasused to form the product of Example 26; and 0.3% w/w SLS was used toform the product of Example 27.

Example 28 Dry Blend Mix of Microcrystalline Cellulose and SLS (0.25%w/w)-Comparative

As a control, EMCOCEL® grade 50 M microcrystalline cellulose (MendellCo., Inc.) and 0.25% w/w SLS powder were dry blended. No spray drying orother treatment of the mixture was undertaken. The method of Example23B, however, was repeated.

Example 29 Processed Microcrystalline Cellulose Without SLS

As a second control, the process described in Example 23B was repeatedexcept that no SLS was added.

Example 30

In this example, batches of compressed tablets were prepared using eachof the products obtained as a result of Examples 23-29. The tablets wereprepared using a Korsch tablet press having a punch size of 3/8" and anaim weight of about 245 mg. The granulations were included in fiveseparate tabletting runs using compression forces of 6, 12, 18, 24 and30 kN respectively. Ten tablets from each run were weighed, measured fordiameter and tested for thickness and hardness on the Erweka TBH 30tablet hardness tester to determine the compressibility of themicrocrystalline cellulose as measured by tensile strength. The resultsof the analysis for the products of Examples 23, 25-29 are graphicallyillustrated in FIG. 6 as a comparison of tensile strength versuscompression force. The results obtained using the product of Example 24were determined to be comparable to that obtained for the product ofExample 25 (0.1% SLS).

As can be seen from the graph, substantial benefits are obtained bycoprocessing Microcrystalline cellulose with SLS. The tablets preparedusing the products of comparative examples 28 and 29 demonstrated poortensile strength. The novel excipient is superior and demonstratesapproximately the same relative improvement across the entire range ofcompression forces. Furthermore, the graph also illustrates that tabletsprepared with a mere dry admixture of Microcrystalline cellulose and SLS(Example 28 formulation) failed to demonstrate acceptable tensilestrengths. Thus, the coprocessed microcrystalline cellulose-SLSdescribed herein provides significant retention of Microcrystallinecellulose compressibility.

Examples 31-32 Docusate Sodium

In these examples, the coprocessing method described in Example 23A wasrepeated except that docusate sodium (Spectrum Chemical) was used as thecoprocessing agent).

    ______________________________________                                        Example     Docusate Sodium (wt %)                                            ______________________________________                                        31          0.25                                                              32          0.50                                                              ______________________________________                                    

The resultant granulates prepared according to Example 23B weretabletted according to the same method described in Example 30 andevaluated for tensile strength. The products of inventive Example 26(Microcrystalline cellulose-SLS 0.20% w/w) and Example 29(microcrystalline cellulose alone) were included in FIG. 7 forcomparison purposes.

Referring now to FIG. 7, it can be seen that coprocessingmicrocrystalline cellulose with docusate sodium also affords theretention of microcrystalline cellulose compressibility.

Examples 33-36 Polysorbate 40

In these examples, the coprocessing method described in Example 23A wasrepeated using the non-ionic surfactant polysorbate 40 (SpectrumChemical) as the coprocessing agent.

    ______________________________________                                        Example     Polysorbate 40 (wt %)                                             ______________________________________                                        33          0.25                                                              34          0.50                                                              35          1.0                                                               36          2.0                                                               ______________________________________                                    

The resultant granulates prepared according to Example 23B weretabletted according to the same method described in Example 30 andevaluated for tensile strength. The products of inventive Example 26(Microcrystalline cellulose-SLS 0.2% w/w) and Example 29(microcrystalline cellulose alone) were included in FIG. 8 forcomparison purposes.

Referring now to FIG. 8, it can be seen that the retention ofcompressibility afforded by coprocessing with polysorbate 40 is wellbelow that provided by sodium lauryl sulfate. In fact, microcrystallinecellulose coprocessed with polysorbate 40 demonstrates compressibilityproperties about the same as off-the-shelf Microcrystalline cellulose inwet granulation formulations.

Examples 37-39 Simethicone

In these examples, the coprocessing method described in example 23 wasrepeated using simethicone (Dow Coming, Midland. Mich.) as thesurfactant coprocessing agent.

    ______________________________________                                        Example     Simethicone (wt %)                                                ______________________________________                                        37          0.5                                                               38          1.0                                                               39          2.0                                                               ______________________________________                                    

The resultant granulates prepared according to Example 23B weretabletted according to the same method described in Example 30 andevaluated for tensile strength. The products of inventive Example 29(Microcrystalline cellulose-SLS 0.2% w/w) and Example 29 (off-the-shelfmicrocrystalline cellulose) were included in FIG. 9 for comparisonpurposes.

Referring now to FIG. 9, it can be seen that this surfactant provideslittle, if any, improvement in the retention of microcrystallinecellulose compressibility. It can, therefore, be seen that mere additionof any lubricant in any amount is not sufficient to allowmicrocrystalline cellulose to retain its compressibility in wetgranulations. Rather, selected surfactants, present within the claimedranges, provide the desirable compressibility characteristics to themicrocrystalline cellulose.

While there have been described what are presently believed to be thepreferred embodiments of the invention, those skilled in the art willrealize that changes and modifications may be made thereto withoutdeparting from the spirit of the invention. It is intended to claim allsuch changes and modifications that fall within the true scope of theinvention.

What is claimed is:
 1. A composition, comprisingmicrocrystallinecellulose; and an effective amount of a compressibility augmenting agentselected from the group consisting of silicon dioxide, a surfactant, ahighly polar compound, and mixtures thereof, provided that when thecompressibility augmenting agent consists of said surfactant, saidsurfactant is present in an amount from about 0.1% to about 0.5% byweight of said microcrystalline cellulose;said composition comprisingagglomerated particles of said microcrystalline cellulose and saidcompressibility augmenting agent in intimate association with eachother.
 2. The composition of claim 1, wherein said compressibilityaugmenting agent provides a hydrophobic boundary at cellulose surfaces.3. The composition of claim 1, wherein said silicon dioxide has anaverage primary particle size from about 1 nm to about 100 μm.
 4. Thecomposition of claim 1, wherein said silicon dioxide is colloidalsilicon dioxide.
 5. The composition of claim 1, wherein said surfactanthas an HLB value of at least
 10. 6. The composition of claim 1, whereinsaid surfactant has an HLB value of from about 15 to about
 50. 7. Thecomposition of claim 1, wherein said surfactant is sodium laurylsulfate.
 8. The composition of claim 1, wherein said surfactant ispolysorbate
 40. 9. The composition of claim 1, wherein said highly polarcompound is a highly polar dye selected from the group consisting of3,3'-[[1,1'Biphenyl]-4,4'-diylbis-(azo)]bis[4-amino-1-naphthalenesulfonicacid] disodium salt; disodium salt of6-hydroxy-5[(2-methyl-4-sulfophenyl)azo]-2-naphthalenesulfonic acid);5-oxo-1-(p-sulfophenyl)-4-[(p-sulfophenyl)azo]-2-pyrazoline-3-carboxylicacid, trisodium salt); disodium salt of1-p-sulphophenylazo-2-naphthol-6-sulfonic acid);trisodium-2-hydroxy-1-(4-sulfonato-1-naphthylazo)naphthalene-6,8-disulfonate);disodium 4,4'-(2,4-dihydroxy-5-hydroxymethyl-3,3-phenylenebisazo)di(napthalene-1-sulfonate)); tetrasodium4-acetamido-5-hyroxy-6-[7-sulfonato-4-(4-sulfonatophenylazo)-1-naphthylazo]naphthalene-1,7-disulfonate);disodium 4-hydroxy-3-(4-sulfanato-1-naphythylazo)Naphthalene-1-sulfonate); trisodium2-hydroxy-1-(4-sulfonato-1-naphthylazo)naphthalene-3,6-disulfonate); andmixtures thereof.
 10. The composition of claim 1, which is prepared in amanner which significantly reduces the hydrogen bonding between inter-and/or intra-molecular cellulose-to-cellulose bonding which occurs whenmicrocrystalline cellulose is exposed to water.
 11. The composition ofclaim 1, which is prepared by preparing an aqueous slurry ofmicrocrystalline cellulose in the form of a wet cake, compressibilityaugmenting agent(s), and other optional ingredients, and drying themixture in a manner which inhibits quasi-hornification.
 12. Thecomposition of claim 10, wherein the drying step is accomplished viaspray drying.
 13. The composition of claim 1, wherein said silicondioxide is included in amount from about 0.1% to about 20% by weight,based on the weight of microcrystalline cellulose.
 14. The compositionof claim 13, wherein said silicon dioxide is included in an amount offrom about 1.25% to about 5%, based on the weight of saidmicrocrystalline cellulose.
 15. The composition of claim 1, wherein saidagglomerated particles have an average particle size of from about 10 μmto about 1,000 μm.
 16. The composition of claim 1, wherein saidagglomerated particles further comprise a member of the group consistingof non-silicon metal oxides, starches, starch derivatives, polyalkyleneoxides, stearic acid, kaolin, polydimethylsiloxane, silica gel,diatomaceous earth, and mixtures thereof.
 17. The composition of claim1, wherein said silicon dioxide portion of said agglomerate is derivedfrom a silicon dioxide having a surface area from about 10 m² /g toabout 500 m² /g.
 18. The composition of claim 1, further comprising anactive agent.
 19. The composition of claim 18, wherein said agglomeratedparticles and said active agent are wet granulated.
 20. A solid dosageform of a compressed mixture of from about 1% to about 99% of anexcipient comprising a particulate agglomerate of microcrystallinecellulose and an effective amount of a compressibility augmenting agentselected from the group consisting of silicon dioxide, a surfactant, ahighly polar compound, and mixtures thereof; provided that when thecompressibility augmenting agent consists of said surfactant, saidsurfactant is present in an amount which from about 0.1% to about 0.5%by weight of said microcrystalline cellulose; and from about 99% toabout 1% of a therapeutically active ingredient.
 21. The composition ofclaim 20, which has been wet granulated prior to compression into atablet.
 22. A method of enhancing the compressibility ofmicrocrystalline cellulose in wet granulation products, comprising:(a)forming an aqueous slurry containing a mixture of microcrystallinecellulose in the form of a wet cake, and an effective amount of acompressibility augmenting agent to improve the compressibility of saidmicrocrystalline cellulose, said compressibility augmenting agentselected from the group consisting of silicon dioxide, a surfactant, ahighly polar compound, and mixtures thereof; and (b) drying said slurryto obtain an excipient comprising a plurality of agglomerated particlesof said microcrystalline cellulose in intimate association with saidcompressibility enhancing agent, provided that when the compressibilityaugmenting agent consists of said surfactant, said surfactant is presentin an amount from about 0.1% to about 0.5% by weight of saidmicrocrystalline cellulose.
 23. The method of claim 22, furthercomprising drying said slurry such that the resultant excipientparticles have an average particle size from about 10 μm to about 1,000μm.
 24. The method of claim 22, further comprising drying said slurrysuch that the resultant excipient particles have a moisture content offrom about 0.5 to about 15%.
 25. The method of claim 22, furthercomprising incorporating into said slurry a member of the groupconsisting of non-silicon metal oxides, starches, starch derivatives,polyalkylene oxides, stearic acid, kaolin, polydimethylsiloxane, silicagel, diatomaceous earth, and mixtures thereof.
 26. A method of preparinga solid dosage form, comprising:(a) forming an aqueous slurry containinga mixture of microcrystalline cellulose in the form of a wet cake and aneffective amount of a compressibility augmenting agent, saidcompressibility augmenting agent selected from the group consisting ofsilicon dioxide, a surfactant, a highly polar compound and mixturesthereof; and (b) drying said slurry to obtain an excipient comprising aplurality of agglomerated particles of said microcrystalline cellulosein intimate association with said compressibility augmenting agent; (c)mixing an active ingredient with said excipient in a ratio from about1:99 to about 99:1; and (d) compressing said mixture obtained in step(c) into tablets; said effective amount of the compressibilityaugmenting agent being sufficient to improve the compressibility of saidmicrocrystalline cellulose, provided that when the compressibilityaugmenting agent consists of said surfactant, said surfactant is presentin an amount from about 0.1% to about 0.5% by weight of saidmicrocrystalline cellulose.
 27. The method of claim 26, wherein saidmixing in step (c) is performed via wet granulation.
 28. The method ofclaim 22, wherein the surfactant is selected from the group consistingof polyoxyethylene compounds, lecithin, ethoxylated alcohols,ethoxylated esters, ethoxylated amides, polyoxypropylene compounds,propoxylated alcohols, ethoxylated/propoxylated block polymers,propoxylated esters, alkanolamides, amine oxides, fatty acid esters ofpolyhydric alcohols, ethylene glycol esters, diethylene glycol esters,propylene glycol esters, glycerol esters, polyglycerol fatty acidesters, SPAN's, sucrose esters, glucose (dextrose) esters, acacia,benzalkonium chloride, cholesterol, emulsifying wax, glycerolmonostearate, lanolin alcohols, lecithin, poloxamer, polyoxyethylene,and castor oil derivatives.
 29. The method of claim 22, wherein thesurfactant is sodium lauryl sulfate.
 30. The method of claim 22, whereinthe wherein the highly polar compound is selected from the groupconsisting of3,3'-[[1,1'Biphenyl]-4,4'-diylbis-(azo)]bis[4-amino-1-naphthalenesulfonicacid] disodium salt; disodium salt of6-hydroxy-5[(2-methyl-4-sulfophenyl)azo]-2-naphthalenesulfonic acid);5-oxo-1-(p-sulfophenyl)-4-[(p-sulfophenyl)azo]-2-pyrazoline-3-carboxylicacid, trisodium salt); disodium salt of1-p-sulphophenylazo-2-naphthol-6-sulfonic acid);trisodium-2-hydroxy-1-(4-sulfonato-1-naphthylazo)naphthalene-6,8-disulfonate);disodium 4,4'-(2,4-dihydroxy-5-hydroxymethyl-3,3-phenylenebisazo)di(napthalene-1-sulfonate)); tetrasodium4-acetamido-5-hyroxy-6-[7-sulfonato-4-(4-sulfonatophenylazo)-1-naphthylazo]naphthalene-1,7-disulfonate);disodium 4-hydroxy-3-(4-sulfanato-1-naphythylazo)Naphthalene-1-sulfonate); trisodium2-hydroxy-1-(4-sulfonato-1-naphthylazo)naphthalene-3,6-disulfonate); andmixtures thereof.
 31. The method of claim 26, wherein the surfacant isselected from the group consisting of polyoxyethylene compounds,lecithin, ethoxylated alcohols, ethoxylated esters, ethoxylated amides,polyoxypropylene compounds, propoxylated alcohols,ethoxylated/propoxylated block polymers, propoxylated esters,alkanolamides, amine oxides, fatty acid esters of polyhydric alcohols,ethylene glycol esters, diethylene glycol esters, propylene glycolesters, glycerol esters, polyglycerol fatty acid esters, SPAN's, sucroseesters, glucose (dextrose) esters, acacia, benzalkonium chloride,cholesterol, emulsifying wax, glycerol. monostearate, lanolin alcohols,lecithin, poloxamer, polyoxyethylene, and castor oil derivatives. 32.The method of claim 26, wherein the surfactant is sodium lauryl sulfate.33. The method of claim 26, wherein the highly polar compound isselected from the group consisting of3,3'-[[1,1'Biphenyl]-4,4'-diylbis-(azo)]bis[4-amino-1-naphthalenesulfonicacid] disodium salt; disodium salt of6-hydroxy-5[(2-methyl-4-sulfophenyl)azo]-2-naphthalenesulfonic acid);5-oxo-1-(p-sulfophenyl)-4-[(p-sulfophenyl)azo]-2-pyrazoline-3-carboxylicacid, trisodium salt); disodium salt of1-p-sulphophenylazo-2-naphthol-6-sulfonic acid);trisodium-2-hydroxy-1-(4-sulfonato-1-naphthylazo)naphthalene-6,8-disulfonate);disodium 4,4'-(2,4-dihydroxy-5-hydroxymethyl-3,3-phenylenebisazo)di(napthalene-1-sulfonate)); tetrasodium4-acetamido-5-hyroxy-6-[7-sulfonato-4-(4-sulfonatophenylazo)-1-naphthylazo]naphthalene-1,7-disulfonate);disodium 4-hydroxy-3-(4-sulfanato-1-naphythylazo)Naphthalene-1-sulfonate); trisodium2-hydroxy-1-(4-sulfonato-1-naphthylazo)naphthalene-3,6-disulfonate); andmixtures thereof.